“Without his help and guidance, there would not have been an AC/DC,” the band acknowledged in an overnight statement. “As a musician, songwriter, producer, advisor and much, much more, you could not ask for a more dedicated and professional man.”

The eldest brother of AC/DC co-founders Malcolm and Angus Young, George was born in Scotland in 1946 but emigrated to Australia with his family as a child. He first rose to local fame in the early '60s as a member of the Easybeats, an Australian band for whom he wrote the late '60s hit “Friday on My Mind.”

Young started his own production company when the Easybeats split in 1970. He and fellow band alum Harry Vanda became two of Australia's best-known pop songwriters, before attracting still wider notice for their production work with AC/DC. They also co-composed "Love Is In the Air," a Top 10 Billboard song in 1977 for John Paul Young.

Albert Music, the publishing company that handled both the Easybeats and AC/DC, confirmed Young's passing. “It is with great sadness that Alberts acknowledge the passing of George Young,” they told the Guardian. “A consummate songwriter, trailblazing producer, artist, mentor and extraordinary musician, George was above all else a gentleman who was unfailingly modest, charming, intelligent and loyal – a man with a wonderful sense of humor. George was a pioneer who, with close friends Harry Vanda and [company namesake] Ted Albert, created a new sound for the Australian music industry.”

Young returned to co-produce AC/DC's 1988 album Blow Up Your Video (with Vanda) and 2000's Stiff Upper Lip, before later retiring. No cause of death was immediately revealed. Harry Vanda added a personal message: “Rest in peace, my dear friend.”